1. Field of the Invention
The present invention relates to an electronic clinical thermometer with a secondary battery serving as a power supply, and more particularly to an electronic clinical thermometer having a configuration and an internal circuit which are suitable for electrically charging a number of such thermometers simultaneously, and a method of and an apparatus for simultaneously charging a number of electronic clinical thermometers powered by secondary batteries.
2. Description of the Prior Art
Known electronic clinical thermometers comprise a thermosensitive element such as a thermistor, a computing and displaying unit, and a battery, all housed in a casing. The computing and displaying unit is composed of a large-scale integration (LSI) circuit for converting a temperature-dependent change in the resistance of the thermosensitive element into a change in the oscillation frequency of pulses, correcting the frequency change to eliminate the effect of the non-linearity of the thermo-sensitive element and converting the corrected frequency change into a reading on the Celsius or Fahrenheit scale, which is then visibly indicated on the display.
Frequent use of such electronic clinical thermometers in hospitals and the like has resulted in employing a secondary battery as a power supply battery for the computing and displaying unit. Various methods are known for charging such a secondary battery used on the electronic clinical thermometer. According to one charging method, the secondary battery is taken out of the casing of the electronic clinical thermometer and then charged by a separate charger. This charging process is tedious and time-consuming particularly in hospitals where a large number of electronic clinical thermometers are used and need to be charged frequently. Another problem is that the thermometer casing cannot be sealed for complete liquid-tightness. The electronic clinical thermometers with such casings fail to withstand sterilization and cleaning with water and chemicals. Another charging process employs a connector for connecting the electronic clinical thermometer to a charger to charge the secondary battery in the thermometer. This charging process is disadvantageous in that the connector tends to develop problems such as contact failure, and in that it is tedious and time-consuming to connect an individual electronic clinical thermometer to the charger. As a result, it is difficult in practice to charge a number of electronic clinical thermometers at the same time.
A large-size electronic clinical thermometer has a charger in its body, and is charged with the charger connected to a commercial power supply outlet. The charger itself is large in size, and each electronic clinical thermometer requires a connector for connection to the commercial power supply outlet. In addition, the electronic clinical thermometer develops contact faults at its connector, and cannot be cleaned and sterilized with ease.
According to still another charging method, an electronic clinical thermometer and a charger, which are physically separate from each other, have coils on bottom and top surfaces, respectively, and the coils are electromagnetically coupled with each other by placing the electronic clinical thermometer that is substantially box-shaped on the charger at a given position thereon for charging the secondary battery in the electronic clinical thermometer. With the above charging method, efficient charging is impossible unless the coils are relatively positioned in an accurate manner for good electromagnetic coupling therebetween, and a plurality of electronic clinical thermometers cannot be charged concurrently. In order to charge a number of electronic clinical thermometers at the same time, it is necessary that as many charger coils be provided as there are electronic clinical thermometers to be charged. As a consequence, the charger becomes large in size to the point where it is impractical for actual use unless a large number of electronic clinical thermometers are to be charged thereby.
The prior charging methods as described above fail to efficiently charge the secondary batteries simultaneously, which batteries are contained in electronic clinical thermometers of the foregoing construction. The conventional charging method and apparatus therefore have largely nullified the advantage of using secondary batteries which need no battery replacement especially in hospitals where a number of electronic clinical thermometers are used.